In recent years, attendant on the spread of networks, documents hitherto distributed in the form of printed matter have come to be transmitted in the form of the so-called electronic documents. Furthermore, in an increasing number of cases, books and magazines have also come to be provided in the form of the so-called electronic publishing. A conventional method for reading these forms of information is to read the information from a computer's CRT (cathode ray tube) or a liquid crystal display.
However, it has been pointed out that in the case of the light-emitting type displays such as CRT, wearing is severe due to a human technological cause so that the system is not suited to long-time reading or the like. In addition, even in the case of light-receiving type displays such as liquid crystal displays, flickering intrinsic of the fluorescent tube is so severe that this system is also not suited to reading. Furthermore, both types of systems have the difficulty that the reading site is limited to the places where a computer is installed.
In recent years, reflective-type liquid crystal displays not using a backlight have been put to practical use. However, the reflectance at the time of non-display (display of white color) in the liquid crystal is 30 to 40%, conspicuously low in visibility as compared with the reflectances of printed matters on paper (the reflectance of OA paper and bunko-size books (Japanese pocket-books) is 75%, and the reflectance of newsprint paper is 52%). In addition, the reflective-type liquid crystal display causes wearing due to glaring of the reflective plate, which is also not suited to long-time reading.
In order to solve these problems, systems so-called paper-like display or electronic paper have been being developed. In these systems, colored particles are moved between electrodes by cataphoresis, or dichroic particles are rotated by an electric field, to achieve coloration. However, these methods have the difficulties that the gaps between the particles absorbs light with the result of bad contrast and that a practical writing speed (within 1 sec) cannot be obtained unless the driving voltage is set to or above 100 V.
As contrasted to the displays based on these display systems, an electrochemical display apparatus (electrochromic display: ECD) based on an electrochemical action is superior in view of higher contrast, and has been put to practical use in, for example, photochromic glass and watch displays. However, the photochromic glass and watch-displays intrinsically do not need matrix driving, so that the electrochemical display apparatus is not directly suited to such display uses as electronic paper. Besides, the electrochemical display apparatus is generally poor in black quality, and the reflectance thereof is on a low level.
In addition, such a display as the electronic paper is, in its use, continuedly exposed to solar light or room light, and, in the electrochemical display apparatus put to practical use in the photochromic glass and watch displays, an organic material is used for forming black portions, which gives rise to a problem as to light resistance. Generally, organic materials are poor in light resistance, and when used for a long time, they show discoloring with the result of a lowering in black concentration.
As a system for solving these technical problems, there has been proposed an electrochemical display apparatus which uses metallic ions as a material for performing a color change. In this electrochemical display apparatus, metallic ions are preliminarily mixed into a polymeric solid state electrolyte layer, and a metal is deposited/dissolved by electrochemical oxidation/reduction, and a color change attendant on this is utilized for display. Here, for example, when a coloring material is preliminarily contained in the polymeric solid state electrolyte layer, the contrast upon the color change can be enhanced.
Meanwhile, for application of the electrochemical display apparatus to such display uses as electronic paper, matrix driving is required. However, in the case of the display utilizing an electrochemical reaction, adoption of a simple matrix driving system gives rise to the problem of unintended coloring due to movement of electric charges. For example, in the simple matrix driving, when (X1, Y1) and (X2, Y2) are selected as shown in (a) of FIG. 8, leveling of electric charges occurs, whereby electric charges move also to (X1, Y2) and (X2, Y1) as shown in (b) of FIG. 8, with the result of coloring there. Particularly, in an electrochemical display apparatus using tungsten oxide or a viologen compound according to the prior art, electric charges are accumulated on an electrode under a colored condition, to generate a potential difference between both electrodes, so that when one pixel is selected and thereafter another pixel is selected, movement of the electric charge occurs, whereby an unintended pixel is colored.
Accordingly, hitherto, it has been considered that the driving system for the electrochemical display apparatus must be an active matrix driving, and the simple matrix driving has not been investigated in practice. However, where the active matrix driving system is adopted, there are the inconvenience that the apparatus would be complicated in constitution and would be extremely high in price.
The present invention has been proposed in consideration of the above circumstances. Accordingly, it is an object of the present invention to enable the simple matrix driving in a display apparatus utilizing an electrochemical reaction, and thereby to provide a display apparatus, and a method of driving the same, in which apparatus constitution can be simplified and the price of the apparatus can be lowered.